Signaling secrecy system



June 23, 1942. M, PHILLIPS SIGNALING SEGRECY SYSTEM Filed June 28 1940INVENTOR 6. M. PH/LL IPS ATTORNEY Patented June 23, 1942 eras SIGNALINGSECRECY SYSTEBI Application June 28, 1940, Serial No. 342,889

8 Claims.

This invention relates to a signaling secrecy system, and moreparticularly to a method of and apparatus for producing noise whichserves to mask signals intercepted in an unauthorized manner fromsignaling apparatus.

A privacy requirement arises in connection with signal apparatus which,incidentally to producing signals for transmission over a lineor othermedium, sets up signal fields in the vicinity of the apparatus and somakes possible the unauthorized. pick-up of signals from these fields,even though access to the line itself or other transmission medium mightbe impracticable. In such cases noise on the line itself Would notprovide the required privacy. Moreover, the use of noise currents on aline to mask the signal requires a noise compensating means at thereceiver to enable the signal to be received and the noise suppressed.

In accordance with the present invention privacy of the indicated typeis provided by use of a masking noise field in the vicinity of theapparatus to be protected from intrusion. This use of a masking noisefield requires no counterpart elsewhere in the system, such as at adistant receiving point, since the noise fields may producesubstantially no eifect on the transmitted currents.

The general object of the invention is to obtain secrecy in theoperation of signaling apparatus.

Another object is to obtain secrecy substantially uniformly in alldirections relative to such apparatus.

A further object is to utilize noise to mask signals independently ofthe signaling equipment.

Still another object is to provide facile means to test theoperativeness of the noise during a normal operation of signalingapparatus.

One type of telephone subscribers set includes an induction coil throughwhich voice currents pass during the transmission thereof to and fromthe respective receiver and transmitter embodied therein. As aconsequence a magnetic field due to such currents is set up in thevicinity of the induction coil. Under certain circumstances suchmagnetic field may be utilized by unauthorized persons to listen in onthe conversations of a telephone subscriber.

In a preferred embodiment as specifically disclosed herein, theinvention comprises a harmonic generator whose output embodies inparallel a plurality of radiating coils arranged such that thelongitudinal axes thereof are-mutually perpendicular.

In series with each radiating coil is such capacity as to provide eachharmonic current with a phase angle such that a magnetic field cluethereto is caused to rotate through 360 degrees in a certain planesubstantially in an elliptical manner, each magnetic field occasioned byeach different harmonic current rotating in a different plane. Thisproduces substantially a composite three-dimensional magnetic field.Accordingly, a superposition of the composite magnetic field on thevoice magnetic field will allow both harmonic noise and voice currentsto be picked up by the unauthorized person but the noise willpredominate in such magnitude as to render unintelligible whateverspeech may also be present.

A feature of the invention is that regardless of the position in spaceof the unauthorized pick-up device relative to the voice magnetic fieldof the subscribers set, the noise will be adequately efiective in alldirections to mask the unauthorized picked-up speech. Another featureincludes an arrangement for instantaneously testing the operativeness ofone or more radiating coils by the subscriber.

The invention will be readily understood from the following descriptiontaken together with the accompanying drawing in which:

Fig. 1 represents a group of magnetic fields produced in accordance withthe action of Fig. 2; and

Fig. 2 is a schematic circuit diagram of an installation according tothe preferred embodiment of the invention.

Referring to Fig. 2, a telephone subscribers set ill including leads H,II connected to a signaling transmission line, not shown, comprises aunitary handset l2 including a receiver [3 and a transmitter I l. Thehandset is mounted on a standard I5 which controls a switch I6 andthereby transmission of voice currents through an induction coil ll.Across the latter is disposed a ringer [8. A dial I9 may also beembodied in the subscribers set. The operation of such arrangement iswell understood, although specific mention is now made that thetransmission of voice currents through the induction coil causes aproduction of a magnetic field in the vicinity thereof. Such magneticfield may be utilized by unauthorized persons to listen in onconversations taking place on the subscribers set.

In the preferred embodiment shown in Fig. 2, the invention comprises anoise generator 25 embodying a source 26 of fundamental Waves,preferably 60 cycles, across which is connected a posed physically thatthe longitudinal axes thereof are mutually perpendicular as shown inFig. 1. In series with the wave distorting device and fundamental sourceis a capacity 34 to tune this circuit to the GO-cycle fundamental Waves.

In the operation of Fig. 2 sinusoidal fundamental waves of 60 cyclesapplied to the wave distorting device occasion therein the production ofa plurality of odd harmonics which are applied to the three radiatingcoils and the capacitors in series therewith. As the capacitors havedifferent capacities, a given harmonic current in the three radiatingcoils is provided with three difierent phase angles. In other words,

the given harmonic current has a diiferent phase ange in each of theradiating coils. This'causes a magnetic field due to each harmoniccurrent to rotate substantially in an elliptical manner through 360degrees in a certain plane. Any pair of radiating coils alone produces arotating magnetic field which lies in the plane of the axes of that pairof radiating coils while the third radiating coil serves to tilt suchnoise rotating field into a plane in which none of the radiating coil.axes lies.

Accordingly, each harmonic current produces a discrete rotatingelliptical-shaped magnetic field disposed in a certain plane, each ofwhich planes is different for the discrete rotating fields occasioned bythe different individual harmonics. The resultant of all such rotatingmagnetic fields is substantially a three-dimensional magnetic fieldwhose efiect is substantially uniform in all directions. Referring toFig. 1, the reference numerals 35, 36, 3'! and 38 represent, for thepurpose of this illustration, the rotating magnetic fields due to a fewof the harmonics. stood that the harmonics produced in the distortingdevice effect substantially similar rotating magnetic fields in theaforementioned manner. The aforedescribed rotating magnetic fields dueto the different harmonics provide noise comprising a number offrequency components extending over the entire speech band or over suchportion of the band as to give effective masking.

The noise generator is physically disposed in relatively close proximityto the induction coil embodied. in the subscribers set so that therotating magnetic fields are superposed on the voice magnetic field.This means that the unauthorized pick-up device, regardless of itsorientation relative to the induction coil, will pick up therein bothharmonic noise and speech currents, but the magnitude of the noise willpredominate to such extent as to mask completely whatever speech mayalso be present. Consequently, the unauthorized picked-up speech isrendered unintelligible by the noise. This arrangement therefore defeatsthe unauthorized interception of speech from the subscribers set.

The pick-up in the telephone set from the magnetic masking apparatus istoo small to be audible. The operativeness of the masking apparatus maybe readily tested by means of a testing circuit 4B which comprises inseries in one It is to be underbranch a manually operated switch 3 I, acapacity 42 and a pick-up coil 63, and in the other branch a manuallyoperated switch 44, a capacity 45 and a pick-up coil G6. Connectedacross both of these branches is a telephone receiver 11. The pick-upcoil Q? has its longitudinal axis in parallel relation with respect tothe corresponding axis of one of the radiating coils, and the pick-upcoil 45 has its longitudinal axis similarly disposed with respect to theaxis of another radiating coil.

Hence, a closing of the switch 4! for example, will enable thesubscriber to hear noise from one radiating coil in the telephonereceiver 41, and a closing of the switch 44 will enable the subscriberto hear noise from the second radiating coil in the same receiver. Thiswould indicate that at least two of the radiating coils are operativefrom which it may be assumed that all three radiating coils are in anoperative condition and, in addition, that the harmonic generator isoperative. If desired, a pick-up arrangement similar to those embodyingthe pick-up coils 43 and 16 may be associated with the third radiatingcoil.

While the invention is described particularly with respect to maskingspeech picked up from the induction coil embodied in a subscribers set,it is not necessarily limited thereto, and is equally applicable to anyvoice apparatus causing the production of voice magnetic fields such asthe ringer and receiver of a subscribers set, a voice repeater, andother signaling apparatus producing a magnetic field thereabout inresponse to a transmission of signaling current.

It will be further understood that the invention is capable ofmodification without departing from the scope of the invention asdefined in the appended claims.

What is claimed is:

1. In combination, a signaling apparatus producing a signaling magneticfield, and means to superpose a plurality of rotating noise magneticfields on said signaling magnetic field to defeat unauthorized detectionof the signaling magnetic field, said means comprising inductancesdifferently oriented with respect to each other to cause the rotatingnoise field to cover all space in the vicinity of and surrounding saidapparatus, and means to energize said inductances.

2. In combination, a signaling apparatus producing a signaling magneticfield, and means to superpose on said signaling magnetic field aplurality of rotating noise magnetic fields having frequency componentsextending substantally over the entire signaling band and whose combinedeffect is substantially uniform in all directions relative to saidsignaling magnetic field and is of sufficient strength to effectivelyprevent unauthorized pick-up of the signal.

3. In combination, a telephone subscribers set producing a voicemagnetic field, and means to superpose a plurality of noise magneticfields on said voice magnetic field, including a plurality of coils anda capacity in series with each thereof to produce a plurality of noisemagnetic fields each of which rotates through 360 degrees in anelliptical manner in a difierent plane, said coils having mutuallyperpendicular axes so that said plurality of rotating noise magneticfields Will have substantially a three-dimensional effect.

4. In combination, a telephone subscribers set including an inductioncoil through which voice currents are transmitted to produce in thevicinity thereof a voice magnetic field, and means disposed in physicalproximity of said set and arranged to produce independently of saidinduction coil a plurality of rotating noise magnetic fields, comprisinga source of fundamental waves, a harmonic producer connected to saidsource, a plurality of radiating coils connected in parallel to theoutput of said harmonic producer and arranged such that the longitudinalaxes thereof are mutually perpendicular, and a capacity connected inseries with each of said coils to provide each harmonic current thereinwith a certain phase angle to cause a rotation of the magnetic field dueto each harmonic current sub stantially in an elliptical manner in acertain plane, each magnetic field due to each harmonic rotating in adifierent plane, said plurality of coils serving to producesubstantially a composite three-dimensional magnetic field whose effectmay be made substantially uniform in all directions relative to saidsubscribers set.

5. The combination according to claim 4 which also includes means totest the operativeness of at least one of said radiating coils, saidtesting means comprising in series a pick-up coil having the longtudinalaxis thereof disposed in parallel relation with respect to thecorresponding axis of the radiating coil to be tested, a capacitor,sound reproducing means and circuit closure means.

6. A protective apparatus for guarding against the unauthorized pick-upof speech signals from a speech magnetic field external of a subscribersset, comprising a plurality of inductance coils to be positioned inphysical proximity of said subscribers set, and circuit means toenergize said coils to generate a plurality of moving magnetic fields ofsufiicient intensity to mask effectively the speech magnetic fieldexternal of said subscribers set said fields having a number offrequency components extending over substantially the entire speechband.

7. In combination, a telephone subscribers set producing an externalvoice magnetic field in the surrounding space, and means to preventunauthorized pick-up of the voice magnetic field comprising a pluralityof difierently oriented magnetic coils, and means to supply said coilswith alternating currents in such phases as to produce rotating noisefields covering all space in the vicinity of and surrounding said set,to effectively mask said voice magnetic field.

8. The combination of claim 7 in which the means to supply said coilswith alternating current includes sources of currents of a number offrequency components extending over substantially the entire speechband.

GEORGE M. PHILLIPS.

